Known methods, in particular of the SMART-CUT® type (as described especially in U.S. Pat. No. 5,374,564) or the like, make it possible to take a semiconductor thin layer from a donor wafer.
These methods are principally based on the use of two steps:
1) formation of a weakened zone or region below one face of the wafer, at a depth corresponding substantially to the thickness of a thin-layer to be transferred to a substrate,
2) detachment of the thin layer from the wafer at the level of the weakened region, the thin layer being the part of the wafer lying on the side of the weakened region next to the face on the detachment side.
This two-step method is generally preceded by a step of preparing or recycling the wafer, which is intended to achieve a surface roughness correction in order to improve the planarity of at least the face of the wafer on the detachment side, but this recycling operation does not generally correct the roughness sufficiently to achieve the manufacturer's specifications for the thin-layer, given that these prerequisite roughness specifications are established with a view to ensuring good subsequent bonding of the detached thin layer onto a support or another layer, and/or in order to finally obtain a layer with a thickness uniform enough to provide a high-quality structure, especially in the case of very thin layers such as in conventional Silicon On Insulator (“SOI”) structures.
A finishing step for roughness correction is therefore normally carried out on the face of the donor wafer on the detachment side to correct the excessive residual roughness after the recycling step so as to comply with the specifications.
The two-step detachment method is then carried out at the face whose roughness was corrected during the finishing step, in order to provide on the one hand a thin layer, optionally bonded onto a support, and on the other hand the donor wafer reduced by the thickness of the thin layer.
This donor wafer can then be reused for the fabrication of a second thin layer after subjecting it to another step of recycling and surface correction.
Although this type of method has provided genuine progress in the fabrication of thin layers, and especially in the fabrication of SOI structures, it is still desirable to improve it, especially in terms of efficiency, speed and fabrication cost, and in particular to reduce the number of fabrication steps.
It would thus be useful to substantially reduce the number of recycling steps required. For example, it would be conceivable to form a weakened region on each of the faces of the donor wafer, then to detach two thin layers simultaneously, as proposed for example in U.S. Pat. Nos. 6,613,678 and 5,856,229, thus avoiding intermediate recycling between two detachments.
Such double implantation followed by such double detachment, however, involves extra technical working difficulties such as the need to turn the donor wafer over in order to form the second weakened region, thus increasing the risk of contamination and electrical and mechanical damage, the need for large and expensive equipment to bond two receptor wafers simultaneously onto the two faces of the donor wafer, and more difficult coordination of the various working steps since both the handling and processing tasks are increased at the same time.
For these reasons, these latter methods do not constitute technical progress in relation to the former ones, but instead lead to undesirable extra technical difficulties.